This invention relates in general to data collection systems and, more particularly, in one embodiment to an improved apparatus and method for monitoring conditions at a predetermined location and collecting data related to such conditions.
During the span of the last decade, there has been a dramatic increase in telecommunications capability on a worldwide basis. Satellite and microwave communication systems, coupled with fully digital telephone switch technology have made it possible for more and more of the world's inhabitants to have access to a telephone, and global telephone service. Indeed, in America and Western Europe almost every residence has access to affordable subscriber telephone service.
In industrialized societies, the role played by telecommunication systems becomes more and more intertwined with the daily operation of these societies. It is nearly impossible to imagine a business office without a telephone, facsimile machine or computer modem to facilitate communication with other similarly equipped offices or industrial centers. In fact, a business without these capabilities is not a viable enterprise from the very start, effectively isolated by an inability to communicate in the most cost effective manner. Therefore, that which began as a convenience evolved rapidly into an economic necessity as technology itself made it economically viable. Consequently, in the face of the ongoing revolution in telecommunications, it becomes less and less profitable to perform tasks manually if the same task can be accomplished by automated methods, particularly if the methods employed are inexpensive.
Corresponding with these developments, the science associated with design of telemetry devices and systems used to collect data from remote sites, via subscriber telephone lines, has developed into a viable technology. This is not to imply that the concept of telemetry data collection is a new idea but rather to emphasize the evolution of an entirely new industry which employs these telemetry techniques to extract the economic and pragmatic advantages gained by the novel application of such methods.
Whereas the word "telemetry" generally brings to mind the transmission of vast amounts of digital (or analog) data from spacecraft or aircraft using exotic signalling technologies, complicated sensors, and wondrous radio communication techniques, the maturation of this fledgling industry has subsequently resulted in the development of telemetry devices which are dedicated to flawless, highly reliable performance at very low costs. This new class of telemetry device is used exclusively in automatic data collection and remote monitoring (ADCARM) systems. In contrast with the readily apparent upheaval in the telecommunications industry, ADCARM systems evolved quietly from systems with initially diverse, archaic or even undefinable objectives into ones with more unified purposes, now with some form of industry standard almost certainly imminent.
Like most viable systems, automatic data collection and remote monitoring (ADCARM) systems must prosper by being more than the merits of a novel concept alone. They do this by providing vital services which cannot be economically duplicated by any other means and, in fact, they triumph when it comes to automating certain types of repetitious tasks. With the wide spread availability of telephone communications reaching to almost every home in the United States, that trend continuing worldwide, there is a natural symbiosis between ADCARM systems and the switched public telephone system to share the resources of that systems already existing infrastructure. Moreover, to encourage cooperation, ADCARM service providers offer risk free revenue incentives to the telephone company by designing telemetry equipment which transparently overlays the existing telephone network, without modification and without any degradation in subscriber telephone service. Hence, when completely installed, some ADCARM systems require only access to the "test trunk" (an existing test port on the central office switch used to test subscriber lines) while, interestingly enough, other configurations require absolutely no access to the central office facilities whatsoever. Consequently, in order capitalize upon the prominent economic advantages gained by sharing the service resources of an already existing telephone network infrastructure, successful ADCARM service providers develop low cost telemetry devices which cannot disrupt the operation of the public telephone network. These remotely located devices simply connect in parallel to the same telephone line which provides the customer with subscriber service thereby providing telemetry capability, typically from the subscriber premises. Compatibility with the existing phone system is assured by designing subservient telemetry devices which relinquish control and automatically disengage themselves under all contention scenarios where a subscriber demands telephone system resources. Since mutual compatibility is an optimal solution, this is the preferred method for implementing ADCARM systems.
There are basically two types of ADCARM systems, called "dial inbound" and "dial outbound". The "dial outbound" system is most frequently employed in automatic meter reading (AMR) systems to collect utility meter readings from customer premises while the "dial inbound" systems are used with vending machine monitors, in addition to AMR applications. The designations "inbound" and "outbound" refer to the method necessary to initiate a telemetry exchange with respect to the central control mechanism for the data system. Thus a "dial outbound" system requires the central data controller (CDC) unit to handshake with (i.e. dial out to) a remotely located telemetry device, to trigger the telemetry exchange. Conversely, a "dial inbound" system is one which "dials in" to the CDC unit under its own volition without requiring any initiating handshake. Most often, "outbound" telemetry units can be called at will since the CDC unit essentially "wakes" them up while "inbound" units, being self-activating, are only available for telemetry exchanges when they "call in" at the designated time. As one might expect, dial inbound telemetry devices often incorporate real time clocks which can be reprogrammed by the CDC unit when they "dial in" at the appointed time.
In contrast to dial inbound units, dial outbound telemetry devices are activated by sending an alerting signal to them while the subscriber line is not being used. Since this signal is designed not to ring the telephone, the user is unaware of the telemetry transaction. Upon reception of this alerting signal, typically a tone burst of specified frequency, the telemetry unit seizes the phone line and completes the telemetry exchange. This procedure, to initiate and collect telemetry data from a dial outbound unit, is very straightforward but does require access to the test trunk at the central office facility. Also in contrast with dial inbound telemetry units, which require a battery to prevent disruption of the real time clock, dial outbound devices can be designed to be completely self-powered from the phone line itself.
Essentially, the dial inbound telemetry unit, like the dial outbound device, is simply another device which plugs into the telephone jack (in addition to the subscriber telephone set) and therefore must not interfere with the operation of the telephone system. Consequently, while the subscriber telephone set is in use, the dial inbound unit cannot be allowed to go off-hook whereby it would attempt to dial over an ongoing phone call. Neither is it desirable that the device become active while the ring signal, intended to "ring" the subscriber telephone set, is present thereby erroneously "answering" an inbound phone call. Because dial inbound telemetry devices only become active at a designated time (some can be activated by an alarm signal applied to special input terminals), it is preferable to view them from a slightly different perspective than dial outbound systems, although their operating requirements are similar. Alternately stated, before a dial inbound telemetry unit becomes active, in response to an activating signal from a real time clock (or an alarm signal), it must first ascertain the status of the subscriber telephone line. If that line is currently being activated by a ring signal or is currently in use by the subscriber the dial inbound unit must wait until the line is again on-hook before it can begin its "dial in" procedure. All dial inbound devices incorporate means to provide these supervisory functions.
Although two basic types of ADCARM devices exist, there is no clear cut rules concerning which telemetry device is best suited to a particular application. In general, however, dial outbound devices are best suited to large scale applications where there is a sufficiently high density of users to justify the installation of hardware at the central office facility. In addition, since these devices can be contacted on an as required basis they are ideally suited to AMR (automatic meter reading) systems which require time-of-day readings, peak period usage, or other events which cannot be scheduled or anticipated in advance. As previously noted, dial outbound systems require access to the test trunk at the central office switch which, albeit a very simple installation procedure, requires approval from the telephone company. If this approval is not forthcoming dial inbound units must be utilized. Since these devices simply dial-in through the conventional telephone network, at a preprogrammed time, into a host computer they require no access to any of the infrastructure of the telephone system. Although dial inbound units are utilized in AMR applications they are best suited for applications which require routine or periodic telemetry exchanges. Some degree of flexibility is afforded to dial inbound units because the next "call-in" time for the telemetry device can be downloaded from the host as part of the telemetry exchange. Still, even with the ability to dynamically select the next "check-in" time, dial inbound devices are not well suited to applications requiring the random collection of telemetry data, because the device is inaccessible until it self-activates.
In certain applications, it has been found that the limitations of the dial inbound telemetry devices are of little consequence, provided that some provision is made to make such devices at least partially responsive to infrequent random access attempts or infrequent random events. Accordingly, some prior inbound devices have attempted to address the problems caused by the inherent nonresponsiveness which inbound telemetry devices exhibit toward random events. For example, some prior inbound telemetry devices can be remotely activated by first ringing the subscriber telephone set and then, after the user answered the telephone, sending an alerting signal, to which the dial inbound system is responsive, to initiate the telemetry exchange. Since the detecting means, responsive to the alerting signal, is not activated until the user takes the handset off-hook, the cooperation of the user is required. Consequently, this particular approach is not suited to applications where the dial inbound telemetry devices are connected to a dedicated telephone line, without any subscriber telephone set or the subscribers themselves to answer the telephone. (It should be noted that this approach is not a hybrid combination of dial inbound and dial outbound technologies since dial outbound units are normally anticipating the reception of an alerting signal only when the subscriber telephone line is not in use.) A further limitation of this approach is a susceptibility for the telemetry unit to be falsely activated by message (voice) traffic on the telephone line, since the device is anticipating the reception of an alerting signal while the phone set is off-hook. Still another limitation, the caller's telephone set must be specially equipped to initiate and couple both the alerting signal and the duplex telemetry data, following initial voice contact with the subscriber. Finally, although not a technical flaw, there is an added expense of designing a detector, responsive to the anticipated alerting signal, as an integral part of the telemetry device. Although the procedure is with flaws the necessity to use it is infrequent and therefore represents an acceptable compromise.
Certain applications, however, require dial inbound telemetry devices to have some local activation capabilities which the devices of the prior art lack entirely. The following example will help illustrate these limitations.
Copy machine monitors are a very good example of an actual industrial application for a dial inbound system. In the business world there exist firms whose sole function is to rent copy machines to other companies or clients. Typically, a monthly fee is charged for the copy machine and an additional fee is levied on a per page basis. In exchange for these payment terms the service provider maintains the machine, keeping it stocked with paper and toner. Some machines, like those placed in libraries or public buildings, may also have coin boxes attached to them for "pay as you go" service. Periodically, say once a month, a customer is invoiced for machine rental and usage.
This application is perfectly suited for a dial inbound system. The copy machine monitor, the remote telemetry unit, incorporates a real time clock which is programmed to activate the device at a certain date and time. At a programmed date and time, the telemetry device, which includes a digital counter to record the number of copies made on the copier, will dial a preprogrammed telephone number to down load this information to a host billing computer. Before going back to "sleep" the device may also receive a new "dial in" time and date from the host system. Conversely, in the event a local alarm condition occurs (low paper-toner, tamper alarm, etc) the telemetry unit will promptly dial into a host computer to report the alarm. Also conversely, say in the event of a paper jam, a push button on the machine may be actuated by the user to summon help. The application is similar for vending machine and pay telephone monitors, which can dial in when the coinbox becomes full or when they are being tampered with. Most devices of the prior art cannot be locally activated except by the real time clock, at the scheduled time, while only a very limited number provide input alarm terminals. Yet, both means for manually activating the dial inbound telemetry unit as well as an electronic means for random activation are very desirable.
FIG. 1 shows a simplified block diagram of a dial inbound telemetry device used for utility meter reading and is believed to be representative of a commercially available device. A further review of FIG. 1 also shows an isolation barrier used to electrically isolate the telephone line side of the telemetry unit from the utility meter side of the device. Since this protects service personnel and equipment alike, the telephone company will not permit the attachment of equipment to their telephone lines unless it provides a specified degree of isolation. To meet these isolation requirements this design uses either optocouplers, which provide optical isolation, or transformers, to provide magnetic isolation. Each isolated side of the telemetry device has a separate battery power source and each has its own independent ground. On the telephone line side of the isolation barrier, a battery is constantly providing bias voltage to the CMOS logic and the circuits which comprise the line status indicator. These are designed to use a negligible amount of power, in a quiescent mode.
On the utility meter side of the isolation barrier is a microprocessor capable of interrogating the electrically encoded meter registers, themselves attached to the bodies of the utility meters. The microprocessor is also capable of programming a real time clock, the device which will activate the dial inbound telemetry unit, and is also capable of formatting the telemetry data for transmission to the remote host. The inbound dialing and data telecommunication functions are implemented by the use of a telephone DTMF (dual tone multi-frequency) dialing device, which generates the touchtones corresponding to the numeric telephone number, and by a modem to transmit or receive telemetry data. It should be noted that the DTMF dialer, modem and real time clock are standard building block circuits which can be purchased from various integrated circuit vendors.
The operation of the dial inbound telemetry device is quite straightforward. Assuming that the device is initially in a quiescent mode (ie asleep), the relay will not be energized and the unit is, in principle, disconnected from the phone line In this mode, no circuit elements on the utility meter side of the isolation barrier are active, with the exception of the real time clock which is always operative. This real time clock is similar to the one used in digital electronic wrist watches, consuming only minuscule amounts of power and is capable of operating for at least a decade on the resident battery. At the appointed time, the real time clock will provide a start pulse which is transferred across the optocoupler to set an RS flip-flop thereby causing its Q output to transition to a logic high level. A "line status circuit" element, is designed to provide a logic high output if the telephone line is available for telemetry use. If the telephone line is available, then the output of the AND gate will set the next RS flip-flop energizing the relay. However, if the telephone line is in use or is receiving a ring signal, the AND gate will prevent the RS flip-flop from being set until such time as the telephone line is available. With an energizing signal now applied to the relay, the contacts close the subscriber loop causing the central office switch to see the phone line as off-hook, drawing loop current. This is equivalent to the subscriber taking his telephone set off-hook and receiving dial tone. The start pulse will also turn the bias circuitry on, thereby enabling the microprocessor, modem and dialing devices. Programming of the microprocessor includes a telephone number which the computer directs the DTMF dialer to dial as part of the "dial-in" procedure. While the host computer is being accessed through the public telephone network, the microprocessor reads the utility meters which are attached to its input terminals and then formats this telemetry data. The modem manages the transmission and reception of duplex data to and from the host computer. Signals from both the modem and DTMF dialer are magnetically coupled across the isolation barrier by a transformer to the telephone line. At the conclusion of the telemetry exchange the microprocessor will generate a stop pulse which turns off bias to all circuit elements on the utility meter side of the isolation barrier, with exception of the real time clock. Simultaneously, this stop pulse is also transferred across the isolation barrier by an optocoupler, resetting both RS flip-flops thereby restoring the telephone line to an idle condition by de-energizing the relay.
Although this is a very simplified approach and not all the elements of a practical dial inbound device are shown, the tutorial does demonstrate the very basic operation of the telemetry unit. In reality, a fail safe timer is usually utilized to automatically disengage the telemetry device after a fixed period of time, to prevent the device from permanently "parking" on the phone line in the event of a malfunction. The practical dial inbound device also contains circuitry to prevent it from being damaged by transients (ie lightning strikes), a diode bridge to make it insensitive to the polarity of the phone line, and usually some circuit elements to prevent nearby radio transmitters from interfering with the normal operation of the telemetry unit. Also, most likely, the mechanical relay would be replaced with a transistor switch. These elements are not shown in FIG. 1, which is intended for tutorial purposes and not for purposes of demonstrating a completed practical design, ready for installation.
In addition, the design shown in FIG. 1 represents only one possible method of implementing a dial inbound telemetry device. Each manufacturer of dial inbound telemetry unit has their own distinct philosophy as to the "proper" design philosophy for implementing these devices. While the device shown is battery powered, some devices are powered directly from the standard wall outlet rather than using batteries. Therefore the exact implementation of a dial inbound telemetry unit is a reflection of many design choices.